.--
BENEFICIAL
N,
OZONE
Ozone - 0 3 - is scarce, even in the strato
sphere where it is most concentrated.But
each molecule counts. Highly unstable
three is a crowd - an ozone molecule
readilysplits up when hit by ultraviolet
radiation(diagramabove). The energy of
the life-damaging UV rays is thus convert
ed into harmlessheat and never reaches the
earth. The breakup leaves a free oxygen
atom- 0
-
and an oxygen molecule - Oz,
the stuff we breathe. The 0 and Oz, in an
ongoing cycle, recombine to form new
ozone molecules.
Long-lived CFCs, unaffected by
rainfallor other naturalcleansing
mechanisms, escape into the strato
sphere within ten years, there to
survive for centuries.
1979
1981
1983
Ozone
under attack
1985
STINGING
POLLUTANT at ground level,
ozone diffused in the stratosphere filters
out much of the sun's harmful ultraviolet
radiation. Over the past decade chemicals, par
ticularly widely used industrial chlorofluoro-
1987
carbons (CFCs), have thinned this protective
ozone around the globe. The loss is greatest
over the South Pole, as seen in these color-
October ozone
concentrations
enhanced images from the Nimbus 7 satellite. (Dobson units)
Here-when sunlight returns in the austral
soo
spring -swirling stratospheric winds and ice
clouds speed ozone's destruction. Concentra
tions within the hole, shown in black, have
325
fallen by as much as 50 percent.
I.50
1989